This invention relates generally to devices for switching radio-frequency signals, and, more particularly, to radio-frequency switching devices with the capability of selectively connecting a plurality of input circuits to a plurality of output circuits.
There are basically two switch configurations with which the invention is concerned. One will be referred to as the broadcast switch configuration, in which N input signals are applied to N corresponding input circuits and each input signal is to be "broadcast" to all of M output circuits. Each output circuit may select from among the N input signals. In the other configuration, referred to as the matrix switch configuration, the N input signals are connected to selected ones of the M output circuits. Regardless of which configuration is considered, a broadcast or matrix switch in general utilizes a large number of cross-connections, and for radio-frequency signals this poses a significant problem of possible interference and "cross-talk" between conductors.
One approach employed in the past to overcome this problem and to maintain sufficient isolation between the circuits has been to arrange the switch in the form of a three-dimensional array. In a first stage of the array there are N circuit boards arranged in a parallel spaced relationship along a first axis of symmetry through and perpendicular to the boards, each of which contains a power divider or switch for one of the input circuits. A second stage, or output stage, comprises M circuit boards also arranged in a parallel spaced relationship, but along a second axis of symmetry perpendicular to the first. In this arrangement, the connections between circuit boards can be made in such a manner as to maintain relatively good isolation between the circuits. However, an obvious drawback of the arrangement is that it is both cumbersome and inefficient in its use of space. Ideally, it would be desirable to fabricate such a switch on a single planar circuit board. However, known planar switches in the digital or telephonic arts are typically extremely complex and do not provide for the high degree of isolation that is necessary for radio-frequency communication. Accordingly, there is still a significant need for a broadcast or matrix switch configured on a single planar board and operable at radio frequencies with a high degree of intercircuit isolation. The present invention satisfies this need.